Conventionally, there is known a resonance phenomenon induced in a space formed by an ear and an earphone/headphone when a user listens to music through the earphone/headphone. Such resonance phenomenon causes the user to hear unnatural sound. Thus, there has been proposed a system for cancelling the resonance phenomenon induced in the space formed by the ear and the earphone/headphone to fix the sound.
However, in the conventional technology, a user may still feel a sense of discomfort even when the resonance phenomenon in the space formed by the ear and the headphone is cancelled, because of the fact that the ear is closed by the headphone.